Soft magnetic materials (e.g., Permalloy) are characterized by high permeability and low coercive forces. They are being used increasingly for electronic article surveillance in department stores and warehouses. For this purpose an alternating magnetic field is emitted into a monitoring zone located preferably in the entrance/exit area of the establishment under surveillance. This field excites the soft magnetic material of the electronic security element so that it emits a characteristic signal. This signal is then detected by a detecting device sensitive to the signal's frequency range and evaluated as an identification signal for merchandise passing the monitoring zone in an unauthorized manner; an alarm is triggered.
The detecting device should no longer respond, of course, once the merchandise has been rightly purchased. This purpose is fulfilled by semi-hard or hard magnetic sections in strip form. Semi-hard or hard magnetic material (e.g., SEMIVAC from the company Vacuumschmelze) displays a relatively high coercive force. As a result of this high coercive force, the alternating magnetic field in the monitoring zone has no effect on the deactivator material in the non-deactivated state. On the other hand, as soon as the deactivator material is driven to saturation by a suitably strong magnetic field--as occurs after the product is rightly purchased--its magnetization prevents the soft magnetic material from responding to the alternating magnetic field in the monitoring zone.
Deactivatable security elements are used in large quantities. Typically, each security element is employed only once for article surveillance, so economical production is a special concern.
From German Patent DE 42 23 394 A1, there is known a method for the production of security labels which includes the following production steps: A hard magnetic metal strip is adhered to a non-metallic ribbon, and a carrier foil of high flexibility in thickness is then adhered to the metal strip. In particular the carrier foil is of a thickness and flexibility suitable to make deformation of the metal strip by a rotating cutter sufficient to sever the metal strip into individual sections. The severed sections of metal strip and non-metallic ribbon are delaminated from the carrier foil, and a soft magnetic ribbon is subsequently applied to the remaining parts of the metal strip. To produce a finished label ribbon, label paper is adhered--as is generally customary--to one side of the ribbon and a carrier ribbon to the other side.
This known method is doubtless ideally suited for supplying large numbers of security elements. Less satisfactory is, however, the relatively high effort needed to manufacture the semi-hard or hard magnetic sections and to apply them to the soft magnetic strips. The waste of semi-hard or hard magnetic material as a result of the cutting operation is also a disadvantage.